This invention relates to a stripper that permits the teeth of a wood incisor to be pulled out of a piece of lumber without tearing the wood.
The process of treating lumber with a preservative typically includes the preparatory step of placing perforations in the lumber's surfaces to increase the depth the preservative penetrates. This is accomplished by running the lumber past incising elements that comprise rotating drums having outwardly-projecting teeth. Such a device is shown in Toberg, U.S. Pat. No. 4,858,660. The teeth are located around the periphery of a plurality of annular incising rings which are separated from one another by annular spacer rings.
Because the effectiveness of the perforations formed by the incisor teeth is directly related to the density of the perforations, it is desirable to place the incisor rings as close together as possible. However, in practice the incisor teeth tend to follow grain lines as they enter the wood and thus often are deflected to one side or the other. If the incisor rings are too close together and two side-by-side teeth happen to bend towards one another, the teeth pinch the wood and when they are pulled back out they tear out a chunk of wood. In fact, several aligned pairs of teeth often combine and cause a segment of wood to be torn free which can result in a long strip of wood being separated from the remainder of the piece of lumber. In either case the lumber is blemished and its strength is diminished making it less valuable, and in the latter case it may be made useless. This problem is described in detail in a paper entitled Effects of Incisinq on Preservative Treatment of Douglas Fir Lumber by J. J. Morrell, S. M. Smith and J. E. Winandy.
The foregoing problem is overcome by the subject invention by placing a stripper element between each side-by-side pair of incisor rings. Each stripper element has a hold-down bar having an outer surface that is generally coplanar with the surface of the piece of lumber that is being incised, but is separated slightly from this surface. The hold-down bar is mounted such that it does not rotate with the incisor drum, and, in a preferred embodiment, the amount of separation between the outer surface of the hold-down bar and the surface of the piece of lumber is adjustable. As the teeth pull out of the piece of lumber, the hold-down bar prevents the upper layer of wood from pulling free from the piece of lumber and tearing does not occur. Thus, the incisor rings can be placed closer together than they otherwise could be and higher penetration densities are obtained.
Accordingly, it is a principal object of the subject invention to prevent the teeth of wood incisors from causing tearing chunks of wood from the piece of lumber being incised even when the teeth are placed close to one another.
It is a still further object of the subject invention to provide a hold-down bar between wood incisor incisor rings which strips the teeth from the piece of lumber without the occurrence of tearing.
It is a yet further object of the subject invention to provide such a hold-down bar in which the distance between the hold-down bar and the surface of the piece of lumber being incised is adjustable.